Safe power generation and flexible power storage is desirable in extended power consumption systems for mobile vehicles, especially underwater vehicles. In many applications it is desirable to have high energy density fuels for extended missions. Examples include submarines where safety and silence are important. Generating useful power without coming to the surface is very important. This class of system is usually called “Air Independent Power” or “Air Independent Propulsion”
In the past, vehicle power systems generated too much noise and were relatively inefficient. Additionally, the power systems were not flexible enough to efficiently satisfy a wide dynamic range of power requirements. In these systems, heat from a hydrocarbon fuel's oxidation was used to drive a turbine, which in turn drove a generator to generate electrical energy. The use of hydrocarbon based fuel introduced additional drawbacks. This type of fuel was dangerous due to the potential for explosion, and in underwater applications, the oxidizer was carried on board and thereby limited the space available for fuel. Only nuclear steam plants which are very large, expensive, and requiring highly trained operators, solved these problems for the world's most advanced Navies.